The invention relates to a rotor bladed disc flange and its layout in a turbo-engine.
Reactor turbines often have to be cooled in order to withstand the heating from the gas from the combustion chamber flowing across them, especially in the first turbine stages. Cooling systems have been developed by ventilation through which the coolest gas is bled off from a portion of the machine upstream from the combustion chamber and blown into the exposed layers of the turbines. In certain special layouts, a flange fixed to the rotor covers the turning disc to be ventilated, under the blade roots, and the gas is blown between the flange and the disc until it enters the borings crossing the periphery of the discs between the blades. Thus, the disc is well ventilated and above all the hottest portions of the periphery.
The flange extends between a hub fixed to the rotor and a free periphery adjacent to the disc and which must be maintained next to it in order to avoid any leaks of ventilation gas. In the state of the art, the centrifugal forces produced by the operation of the machine deform the flange by separating it from the disc, which breaks the seal and requires the use of hooks on the disc to remedy this, under which the flange edge is engaged. However, the hooks have a disadvantage in that they raise the manufacturing costs of the disc and are fragile.
A flange assembly in which the edge is retained by hooks on the disc is described in the document U.S. Pat. No. 4,466,239, in which the flange is practically plane.
An analysis of the action of the centrifugal forces leads to detailing the shape of the flange. Generally, there is a principal flexion zone for the flange sections in an axial plane, whose position is greatly responsible for the behaviour of the flange assembly under the effect of centrifugal forces, even if all the portions of the flange are submitted. This zone resembles a pivot beyond which the flange remains approximately non-deformable and beyond which it deforms much more either because of its flexibility or because of its distance from the axis of rotation. Thus a normal shape for the flange comprises, from the flat hub where it is fixed to the rotor, an arm in the form of a tubular sleeve, and then a closely flat web. The arm is lightened by making it almost as thin as the web; the principal flexion zone then tends to be on the arm, which deforms by opening on the web side; this then tilts moving away from the disc.
This is why the patent WO-99 32761 proposes a different layout; where the flange is essentially deprived of the sleeve and essentially comprises, after the hub, a very rigid bulged part and then an increasingly thin web inclined when moving away from the disc. The flexion zone is inclined moving away from the disc. The principal flexion zone is then located on the web; furthermore, the flange is provided with a flyweight near the periphery of the web, beyond the principal flexion zone and which protrudes from the diverted side of the disc: the centrifugal forces result in straightening the flange by reducing the inclination of the portion including the flyweight, thus pressing the free end of the flange tightly against the disc. The maintenance hooks thus become superfluous. Nonetheless, the flyweight represents a considerable extra weight for the flange.
Thus, according to the invention, the aim is to obtain a similar effect for tilting the flange under the action of the centrifugal forces but without this effect being produced by a special part. It is proposed instead to use what are called labyrinth seal lickers, often found in turbo-reactors to establish a seal all along the flange.
The lickers of a labyrinth seal comprise a portion of sleeve or junction with the support part of the licker and a cutter portion which tapers towards a free end and establishes the seal by penetrating a crown of easy erosion (xe2x80x9cabradablexe2x80x9d) material fixed to the other part connected by the joint. Contrary to the usual construction where the licker knives are arranged radially outwards towards the exterior, here they are inclined axially moving away from the disc, which off-centres them and thus increases the tilting moment towards the disc produced by the centrifugal forces at the edge of the flange. Furthermore, axial and radial shifts of the cutter parts of the lickers are adopted so as to increase the off-centring of the lickers and to adjust the overall effect of the centrifugal forces by distributing them over the web. It will be seen below that this staggered arrangement also facilitates licker manufacturing.
To resume, the invention in its most general form relates to a rotor bladed disc flange, comprising a hub fixed to the rotor and a web covering one face of the disc and having a periphery adjacent to the disc, and original in that it comprises, on one face of the diverted web of the disc, a plurality of labyrinth seal lickers comprising cutting parts inclined towards an axial direction of the rotor and moving away from the flange towards the tapered ends of the cutter, the cutter parts of the lickers being staggered axially and radially from each other, the web and the lickers having, in an axial section, a centre of inertia separated from the disc by a radius passing through a principal flexion zone of the flange.
According to the invention, the web of the flange is the peripheral portion of this flange which covers the disc and which is characterised by having a big radial width and being sufficiently slender so that it can bend when submitted to centrifugal forces from the rotor. It thus comprises the principal flexion zone and the zones located beyond this, as far as the edge of the flange.
A portion of the web carrying the lickers can be inclined in the axial direction of the rotor moving away from disc towards the periphery adjacent to the disc, in order to encourage straightening of the web under the effect of the centrifugal forces and to reinforce the bearing of the periphery of the flange on the disc.
Other layouts according to the invention, secondary but nonetheless useful, make it possible to adjust or reinforce the bending of the web in the required direction while still enabling it to be ventilated efficiently.